Set union of Datastores with TransformedDatastores

Given an imageDatastore and some transformation of it, e.g.,

imds1 = imageDatastore({'street1.jpg','peppers.png'});

imds2 = transform(imds1,@(x) imwarp(x,tform));

I would like to form the set union of these data stores in some way so that trainNetwork processes the series of images from both imds1 and imds2 as a single combined set (and similarly with the response data). Is this possible in some way?

I am aware that this functionality is somewhat captured by augmentedImageDatastore, but the operation I describe would open up a variety of data augmentation schemes not currently avaialble.

I am also aware of this thread,

https://www.mathworks.com/matlabcentral/answers/327026-how-to-join-or-merge-two-image-data-stores?s_tid=answers_rc1-2_p2_MLT

but this does not cover what I am pursuing here, because the images in a TransformedDatastore are not physically stored anywhere (nor would I want them to be).

Answer 1

[Jeremy Hughes]

Horizontal (i.e. associated reads)

-----------

cds = combine(imds,otherds);

Vertical (i.e. joining two sets of files into one datastore)

-----------

imds = imageDatastore({'folder1/*.jpg','folder2/*.png'});

Or leave off the extensions

imds = imageDatastore({'folder1/','folder2/'});

[Matt J]

Thank you, Jeremy. But no, that is not what I am looking for, unless I'm misunderstanding what combine does. In what I am looking for, the total population of training images would be formed from the union of the set of images in imds with the set of images in otherds.

[Jeremy Hughes]

Ahh, you can specify multiple folders in imageDatastore. This creates one datastore from both sets of files.

imds = imageDatastore({'folder1/*.jpg','folder2/*.png'});

Or leave off the extensions

imds = imageDatastore({'folder1/','folder2/'});

[Jeremy Hughes]

updated the answer

[Matt J]

Ahh, you can specify multiple folders in imageDatastore.

Yes, I can see that will work for joining two ordinary imageDatastores, but what about an imageDatastore and a TransformedDatastore, like in my posted example,

imds1 = imageDatastore({'street1.jpg','peppers.png'});
imds2 = transform(imds1,@(x) imwarp(x,tform));

As I understand it, imds2 does not store the transformed images in a physical folder, so you cannot simply list additional folders to capture its images in the training set.

[Jeremy Hughes]

I see.

imds2 = transform(imds1,@(x) {x;imwarp(x,tform)});

This would return both images, but then they'd always be returned together, which isn't really what you want for trainNetwork (I assume).

You could write the images out to disk by calling read on imds2 and passing the results to imwrite, but you'd need to have unique file names. You could use the second output of read to get the file names. This is a bit of coding.

The only other way I can think to do what you're looking for would be to create your own datastore with https://www.mathworks.com/help/matlab/import_export/develop-custom-datastore.html

Your datastore would hold onto both the original datastore, and the transform, and just return reads from one until it's done, then the next one until it's done and so on.

[Matt J]

That looks like what I want!

Just out of curiousity, though, is it possible to do the customization by inheriting from imageDatastore, rather than matlab.io.datastore, as the example at your link shows?

[Carlos Ramirez]

Hi, did you ever manage to solve this ?. I don't really understand what's the purpose of the function combine(idms,idms2) (with idms2 being a transformed one) if later the read function returns two images at the same time. How useful is that for training a CNN using trainNetwork ?. Similat to the original question, I do not want to physically store the augmented images created by the transform function. Any help ?